The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
A Power Amplifier (PA) may at times have a gain different than a desired gain. A gain compression occurs when the PA gain is lower than the desired gain and a gain expansion occurs when the PA gain is higher than the desired gain. Variation in a PA power output and/or a PA supply voltage may cause gain compression or gain expansion. This may cause a system intended to operate with a constant gain (“an iso-gain system”) to deviate from operating as intended.
Envelope tracking (ET) includes modulating one or more PA supply voltages according to a transmit (TX) signal envelope. ET may be used to increase PA efficiency when the TX signal has a high Peak-to-Average-Power Ratio (PAPR). ET may also be used to produce iso-gain operation of a PA.
A time alignment (TA) is a measure of the difference between a change in the TX signal envelope at the input of the PA and a corresponding change in a PA supply voltage. A mismatch of the TA occurs when the change in the TX signal envelope at the input of the PA occurs before or after the corresponding change in the PA supply voltage.
When the gain of the PA is dependent on the PA supply voltage or the PA power output, a mismatch of the TA produces a distortion in an output signal of the PA. The distortion in the output signal may produce interference between neighboring communication channels, including interference characterized by an Adjacent Channel Leakage-Power Ratio (ACLR).